The structure of the accreted mass in the HMXB Vela X-1, consisting of a neutron star and the high mass donor star HD 77581, is investigated by analyzing the flaring behavior in X-rays.
To this end we analyzed all archival INTEGRAL data, calculating the brightness distribution in the 20–60 keV band. We show that the emerging distribution is closely following a log-normal distribution. Orbital resolved analysis shows that the structure in the accretion region is strongly variable, explainable by shocks and an accretion wake. Analysis of RXTE ASM data shows a strong orbital change of NH. Derived accreted clump masses from the INTEGRAL data are of the order of 1020–1021 g. We show that the lightcurve can be described using a model of multiplicative random numbers.
In course of the simulation we calculate the Power Spectral Density of the system in the 20–100 keV energy band and show that it follows a red-noise power law.
We conclude that a mixtures of a clumpy wind and shocks and turbulences can explain the measured distribution.